A working knowledge of C++, plus a bit of online reading about CUDA and the NVidia GPU architecture, plus studying the LCZero chess engine source code (the CUDA neural net part, I mean) seems like enough to get started. I did that and felt like I could contribute to that code, at least at a newbie level, given the hardware and build tools. At least in the pre-NNUE era, the code was pretty readable. I didn't pursue it though.
Of course becoming "really good" is a lot different and like anything else, it presumably takes a lot of callused fingertips (from typing) to get there.
Of course becoming "really good" is a lot different and like anything else, it presumably takes a lot of callused fingertips (from typing) to get there.